Lead exposure is a significant environmental hazard which can affect large and diverse segments of the population. For example, exposure can occur to workers involved (and others in the area) in removal of lead based paints and/or the renovation of structures containing lead based paints, workers in metal working and other metal related industries, workers in other industrial facilities, as well as adults or children living within or visiting homes or schools containing lead based paints Prolonged and repeated exposure to workers involved in removal or abatement of lead based paints and exposure of children in homes and schools is especially damaging. Lead residues on human skin, especially on the hands, of industrial workers (as well as others) can be a significant health risk since such residues may be ingested during normal activities (e.g., eating, drinking, and smoking). Although hand washing, if done carefully, can remove a virtually all lead residues, it is difficult for individuals to quickly and easily determine the actual effectiveness of the hand-washing process and, most importantly, to assess if significant lead residues remain on the hands after washing.
Several chemical spot tests for the detection of lead in air, water, soil, dust, paint, and similar samples are available. Generally, such tests are based on the reaction of lead with either rhodizonate or sulfide ions. For example, U.S. Pat. Nos. 5,416,028 (May 16, 1995), 5,445,965 (Aug. 29, 1995), 5,496,736 (Mar. 5, 1996), and 5,567,619 (Oct. 22, 1996) provide methods for determining lead in liquid samples. U.S. Pat. Nos. 5,039,618 (Aug. 13, 1991), 5,330,917 (Jul. 19, 1994), 5,364,792 (Nov. 15, 1994), and 5,550,061 (Aug. 27, 1996) provide methods for detecting lead using a test swab impregnated with a test reagent. The test swab is rubbed over the surface to be tested; if lead is present on the tested surface, the swab will exhibit a characteristic color. Such a test swab based on the lead and rhodizonate ion reaction system is used in the commercially available lead testing kit Lead Check.TM. available from HybrilVet Systems, Inc. of Natick, Mass. In the Lead Check.TM. system, two reagents (sodium rhodizonate and a tartrate buffer) are contained in glass or plastic tubes separated by an inert spacer. When activated, the reagents are mixed and then used to saturate an absorbent (i.e. cotton) tip of the swab (thereby producing a yellow color). By rubbing the cotton tip over the surface to be tested, the presence of lead can be detected by observing the color of the swab tip (a pink to red color indicates the presence of lead, the lack of any color change indicates the absence of significant levels (e.g., less than about 2 .mu.g) of lead).
Generally such chemical spot tests or methods cannot be used to directly determine the presence of lead on human skin or to directly evaluate the effectiveness of various removal techniques (e.g., hand washing) for removing lead from human skin. For example, the Lead Check.TM. system, if applied to human skin testing, would involve wiping the swab directly on the skin and thereby exposing the skin to the test reagents. Moreover, to fully evaluate the presence of lead on the skin and/or test the effectiveness of lead removal, large areas of skin would require exposure to the test reagents. For example, to fully evaluate the effectiveness of hand washing for the removal of lead, a large portion of the hands would have to be swabbed with careful attention to areas around and under the nails and cuticles. In addition to possible skin discoloration due to the reagents (e.g., yellowing caused by sodium rhodizonate), skin irritation and damage is possible because, for example, of acids which may be present in the test reagents. Moreover, the long-term effects of such exposure to sodium rhodizonate (especially where repeated testing is necessary or desirable) is not known. Thus, testing for human exposure is normally done by indirect means such as, for example, by evaluating surfaces in which workers or other individuals, if contaminated with lead, would likely come into contact with and, therefore, transfer lead onto. Thus, for example, car steering wheels can be tested to indirectly estimate exposure of workers' hands to lead. Such indirect methods, however, can miss or under report significant human exposure. Such indirect methods, although they may reduce the exposure to test reagents, do not eliminate such exposure. Even when used for normal test surfaces (i.e., tables, window sills, steering wheels, and the like), the test operator's skin can be exposed to the test reagents. Moreover, unless careful cleaning methods are used to remove test reagent residues from the tested surfaces, individuals who later contact the surfaces may also be exposed to the reagents
It would be desirable, therefore, to provide a safe, reliable, and direct method for testing for lead exposure on human skin which would avoid exposure of the skin to the test reagents. It would also be desirable to provide a safe and reliable method for testing for lead exposure on other surfaces which would not leave reagent residues on the test surfaces. It would also be desirable to provide a safe, reliable, and direct method for determining the effectiveness of lead removal from human skin. The present invention provides such methods.